Preformed particle gel for conformance control in an oil reservoir

ABSTRACT

Expandable and hydrophilic polymeric particles may be made in a non-emulsion system, and with controllable hardness and delay in their time to swell in a fresh or salt water environment. These particles are prepared from combining monomers, controlled monomers, stable cross-linkers, initiators, and other agents, in aqueous solution. The controlled monomers induce kinetically controllable decomposition, degrading over time, thus inducing a desired time delay in particle swelling. The delay and degree of the swelling of the particles is controlled by selection of controlled monomer, stable cross-linking agents, monomers, and process conditions. These preformed particle gels are made to an initial particle size of 0.1 micron in diameter or larger via different grinding techniques. This composition is used for modifying the permeability of subterranean formations and thereby increasing the recovery rate of hydrocarbon fluids present in the formation.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/780,950, filed on Feb. 28, 2006, which is hereby incorporated byreference in its entirety as fully set herein.

FIELD OF THE INVENTION

The present invention relates to the field of hydrocarbon production.Particularly, the present invention relates to the manufacture ofparticles with improved physical and chemical characteristics that whenadded to injection water will further improve the crude hydrocarbonrecovery from subterranean heterogeneous reservoirs.

BACKGROUND OF THE INVENTION

Many reservoirs from which oil and gas are produced are not homogeneousin their geologic properties (e.g. porosity and permeability). In fact,for many of such reservoirs, the differences in the permeability(ability to allow fluid flow) among the different geologic layers canvary as much as several orders of magnitude.

Commonly a fluid, particularly water, is injected into an injection wellcompleted into an oil reservoir. The injected water will mobilize andpush some of the oil in place to a nearby production well where the oiland injected fluid are co-produced. A wide variation in the permeability(a property that measures the ability to transmit flow) among thegeologic layer of rock that contain oil within its porous spaces in thesubsurface reservoir causes such water injection to be not uniform, withthe larger proportion of the water entering into the higher permeabilitygeologic layers. This condition results in a very non-uniformdisplacement of the oil within the reservoir, with most of the oilquickly mobilized from high permeability layers and little from thelower permeability layers. The result is the fluid exiting productionwells will have quickly a high percentage of water and less and lessoil. The displacement process reaches the economic limit when the levelof produced water is too high, and not enough oil is recovered, at atime when a large volume of oil remains in the bypassed, and not yetswept, lower permeability regions of the reservoir.

FIG. 1 illustrates the common situation of an oil reservoir having anundesirable distribution of injected water and poor coverage of targetsubterranean formations containing crude oil. FIG. 1 represents a sideview of a geologic formation between an injection and production well.Item 1 represents a stream of pressurized water being forced into theinjection well 2. The well bore is completed so that there is no openinginto non-oil bearing geologic interval 3. Openings are present in thewell bore across the oil bearing geologic formations 4 and 5. Formation4 has much higher permeability than formation 5. In the situationdepicted, the much larger fraction of the injected water 6 enters andexits the higher permeability formation 4. Little of the injected water7 enters and exits from Formation 5. This is an undesirable resultbecause any free oil in the high permeability formation is recoveredquickly, but little of the oil from the lower permeability formation 5.The result is that the total produced stream 8 (a mixture of the fluidsfrom both formation 4 and 5) quickly has a very high percentage of waterand little oil that proceeds up the well bore of the production well 9.This behavior causes the process of water injection to become uneconomicsoon, and there is still a high crude oil content left behind in thelower permeability formation 5.

One approach to improve the oil displacement process is to provide somemeans to block, or at least significantly increase the flow resistance,selectively in these very high permeability geologic zones, sometimescalled “thief zones”. If a process is successful in accomplishing thisobjective, then the water injected thereafter is diverted to enter nowpreferentially other geological layers of rock with lower permeability.This then forces the water to displace oil not before contactedsignificantly by the injection fluid. Such a process to make theinjected fluid, such as water, sweep the oil reservoir in a more uniformfashion has been called “conformance control”.

Conformance control processes for an injection well are applied usuallyafter offset production wells begin to experience a high fraction ofwater in the produced fluids. Recently, the research of injection fluiddiversion has developed some chemical processes in which plugging agentsare added to the injection water. These chemical systems have includedbulk gel, sequential injection for in-situ gel formation, and colloidaldispersion gel (CDG). Bulk gel refers to adding polymer and across-linker to water and allowing some gel reaction to occur. Thisfluid is injected into an injection well for some period of time,followed by normal water injection. Another variation is to inject slugsof polymer solution and cross-linking solution separately, and thenhaving a blocking gel form inside the reservoir as these chemicals mixtogether and react in-situ. The CDG process has a low concentration ofpolymer and cross-linker added together to the injection water beingagitated at the surface. The process with a partial gel reaction andmixing at the surface creates fine particles before injection of thisfluid. The concept is that the chemical components in this fluid willfurther react and create a stronger blocking gel in-situ.

However, these chemical conformance control methods have significantdisadvantages: the bulk gel process described above requires highconcentration of both polymer and cross-linker chemicals to make astrong gel, and the gelation time and physical properties are difficultto predict; sequential injection of polymer and crosslinker solution isquestionable regarding controlling the time to create a gel in-situ andthe strength of the gel that might form; colloidal dispersion gel (CDG)and the other previous methods described are unstable at more extremereservoir conditions and therefore inadequate for reservoirs with hightemperature (greater than 90 degree C.). In addition, the CDG is notsuitable when the salinity exceeds 5000 ppm Total Dissolved Solids (TDS)and it is not able to block effectively the very high permeabilitychannels.

Another, more recent, chemical approach that is gaining favor because itdoes not have the above disadvantages is the so-called PreformedParticle Gel (PPG) technology. The PPG particles typically are a powderproduct made up of a cross-linked polymer that will swell after theiraddition to a fresh or salt water. For their application the PPGparticles are added to the injection water for some period of time, andthen followed by normal water injection. These soft, swollen particlesdispersed into an injected brine have the desirable property that astheir suspension is injected, they will block the flow pores of thetarget, very high permeability geologic layers in a reservoir that havelittle oil remaining. Advantages of the PPG approach versus the otherchemical systems described above include that the PPG product added hasa known chemical composition, and that a PPG suspension in the injectionwater created at the surface will have predictable physical properties.In addition, these PPG suspensions can be stable and perform theirdesirable partial plugging action in the highest permeability zones ofthe reservoir at harsher reservoir conditions (up to 120 degree C. andin a brine containing up 300,000 ppm TDS).

The PPG technology, however, has two important limitations. First ofall, these PPG particles swell almost immediately when exposed to water.This means that their desirable selective plugging action is confined tonear the injection well, and thus these swollen particles are not ableto penetrate deeply into the reservoir. This limits the volume of thereservoir that can be treated to divert the injection water into thelower permeability areas that contain high oil content. Secondly, thePPG particles commercially available have a relatively large size(hundreds of microns to millimeters in diameter). This limits theirapplication to plugging only very high permeability (tens of Darcies)layers. In some cases the problem, highest permeability layer is not sohigh, perhaps less than 10 Darcies. In that case it would beadvantageous to have a starting particle of a smaller size, in the rangeof tens of microns.

U.S. Pat. No. 5,662,168 (1997) by Smith discloses the process involvesthe use of a water soluble polymer in conjunction with an aluminumcitrate preparation to function as a cross-linker for the polymer.However, it fails to realize the possible chromatographic separation inthe subterranean formations when unreacted polymer and this crosslinking agent are injected in separate solutions sequentially. Thisseparation of components can cause the inefficient cross-linkingreaction and only a very weak gel in-situ.

Representative preparations of PPG, cross-linked polymeric particlesusing various monomers, fillers, cross-linkers and initiators aredescribed in CN Pat. No. 1,251,856A, 1,552,793A, 1,796,484A, and1,439,692A. Liu, Y., et al. Paper SPE 99641 (2006) describes the commonparticle can only be injected into and move through those porous mediawith permeability of about 10 Darcies or greater. The Bai, et al, paperSPE 89468 (2004) discusses about the particle gel propagation behaviorsthrough pore throats at both microscopic and macroscopic scales.Particle gel can move through porous media only if a driving pressuregradient is larger than a threshold pressure gradient. The chemistry ofthe above patents only describes a single cross-linking agent in theparticles, particles of very large size (as much as millimeters indiameter), and that the particle gels swell as soon as they are mixedinto water. Hence their applications will be only near the injectionwell bore and or for reservoirs with thief zones of very highpermeability zones or fractures.

U.S. Pat. No. 5,465,792 (1995) and U.S. Pat. No. 5,735,349 (1998) byDawson et al. (BJ Services) disclose the use of swellable cross-linkedsuperabsorbent polymeric microparticles for modifying the permeabilityof subterranean formation. However, swelling of the superabsorbentmicroparticles described therein is induced by changes of the carrierfluid from hydrocarbon to aqueous or from water of high salinity towater of low salinity. The patents are not for preformed gel. All theirexamples and claims are for water soluble polymer in an emulsioncondition. U.S. Pat. No. 6,454,003B1 (2002), U.S. Pat. No. 6,729,402B2(2004) and U.S. Pat. No. 6,984,705B2 (2006) by Chang et al. disclose acomposition comprising expandable cross-linked polymeric microparticlesto be used for modifying the permeability of subterranean formations.Large percentages of surfactant are required for preparation of themicroparticles via emulsification, which increases the product costsubstantially. In addition, there is an additional environmental issueby including the surfactant, not to mention the added complexity ofworking with an emulsion system to make the product. The unexpandedparticle size can only be as large as 10 micron due to the limitation ofthe microemulsion system. Such small particle may get into the lowpermeability matrix target zones and inadvertently plug areas rich inresidual oil. Again, the system disclosed in these patents involvesmicroemulsion rather than preformed gelation. Having a microemulsionwill significantly increase the cost of the treatment product. Moreover,the micron level particle size makes the product less desirable fortreating very high permeability zones or fractured reservoirs.

According to the previous references, a need exists for improving thefull potential of performing in-depth conformance control treatment. Forin-depth conformance control, adjustable initial particle size innon-emulsion solution with low threshold pressure is favorable.Moreover, none of the references cited consider an expandable andhydrophilic polymeric particle made in a non-emulsion system that hascontrollable size, hardness, and swelling delay when added to freshwater or a salty brine.

SUMMARY OF THE INVENTION

The present invention is a controlled particle that has a preferred sizerange from 10 micron to 5 millimeters. These expandable and hydrophilicpolymeric particles are made in a non-emulsion system. Furthermore theyhave the property of allowing their swollen state in a fresh or saltwater to be delayed to a specified time under different reservoircondition and to a controllable extent.

These particles are prepared from a chemical reaction involving one ormore polymerizable monomers (typically acrylamide monomer), one or morecontrolled monomers whose decomposition is kinetically controllable, oneor more stable cross-linkers, initiators, bases, reducing promoters,regulators, stabilizers, chelating agents, thermal agents,chain-transfer agents, oxygen scavengers, pH adjusters, and gel strengthmodifiers in aqueous solution. The selection of the reactants,especially the controlled monomers and their concentration will controlthe delay time before the onset of particle swelling and also influencethe extent and physical properties of the swollen particle, when suchparticles are added to fresh or salt water.

Several methods may be employed to reduce the size of the createdparticle gel to a desired size. These include, but are not limited to,mechanical methods (such as fluid energy or jet mills, stirred mediamills, ball mills, colloid mills, vibrating mills, rotor mills, cuttingmills, disc mills, jaw crushers, and mortar grinders), physical methods(such as spray drying), or chemical methods (polymerization insuspension). Such practices may reduce the initial size of theseparticles to be as small as 0.1 micron in diameter.

These gel particles may be especially advantageous when used asselective plugging agents added to fresh or salt water injected into anoil reservoir. The features of having a controllable time delay beforesignificant onset of swelling in water, and their smaller initial sizegive them the desirable capability to block target higher permeabilityrock layers further from the injection well than otherwise.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is to improve on the current particle and geltechnology for selective plugging of high water flow channels in oilreservoirs. The Controlled Particle Gel (CPG) composition of the presentinvention is designed to overcome the main drawbacks of the in-situgelation systems, which are lack of control of the timing and the extentof the gelation and flow resistance effect due to adsorption, dilutionor degradation of the polymer, pH change. In addition, these chemicalsystems have limitations in their lack of stability to high temperatureand salinity. The process disclosed here also is superior to the currentPreformed Particle Gel (PPG) products that have little or no delay intheir swelling behavior and are available only in sizes of hundreds ofmicrons in diameter or larger. The CPG particles have the improvedproperty that their delay in swelling time and extent may be controlled.This enhanced feature is due to the incorporation of a controlledmonomer, which will decompose over a designed period of time that thentriggers the significant expansion of the particles. Another improvementdisclosed in the present invention is that any particle gel may bereduced in size to a diameter as small as 0.1 microns by mechanical,physical, or chemical methods. These improved properties allow suchpreformed particle gels to penetrate farther into an oil reservoir.

The adverse results illustrated in FIG. 1 may be improved by theinjection of a water treatment fluid containing Controlled Particle Gel(CPG). The suspended particles will enter and plug preferentially thevery high permeability formation 4. In particular, with CPG particleshaving their designed delay in swelling time, and their initialrelatively small particle size, they will penetrate a significantdistance from the injection well 2 into the high permeability formation4. Once in this formation environment for a designed period of time, theCPG particles will begin to swell and thereby plug significantly thevery high permeability formation 4. Provided the permeability of theformation 5 is low enough (substantial contrast in formationpermeability between 4 and 5), the initial size of the CPG particles maybe selected so that they have the desirable outcome of being largeenough not to enter into formation 5, while still being allowed topenetrate deeply before they swell into the high permeability formation4.

FIG. 2 illustrates the improvement in a water injection process of anoil reservoir after completing a treatment of Controlled Particle Gel(CPG). The numbers and their general meaning are the same as FIG. 1.FIG. 2 represents a side view of a geologic formation between aninjection and production well. Item 1 represents a stream of pressurizedwater being forced into the injection well 2. The well bore is completedso that there is no opening into non-oil bearing geologic interval 3.Openings are present in the well bore across the oil bearing geologicformations 4 and 5. Formation 4 had much higher permeability thanformation 5 originally, but after the CPG treatment, now formation 4 hasa much lower permeability to injection water than previously. Thisalteration in the geologic permeability now causes a much smallerfraction of the injected water 6 to enter and exit the higherpermeability formation 4. Most of the injected water 7 instead entersand exits from Formation 5. This is a desirable outcome because now mostof the injection water 1 will contact and mobilize more of the free oilpreviously untouched. The result is that the total produced stream 8 (amixture of the fluids from both formation 4 and 5) soon will have animprovement with a lower percentage of water and more oil that proceedsup the well bore of the production well 9.

The CPG particles for this invention may be made by reacting monomers,controlled monomers, stable cross-linkers, initiators, bases, reducingpromoters, regulators, stabilizers, thermal agents, chain-transferagents, oxygen scavengers, pH adjusters, gel strength modifiers, inaqueous solution under non-emulsion condition In the disclosure of CPGpreparation, the term “Monomer” refers to nonionic monomer, anionicmonomer, cationic monomer, zwitterionic monomer, betaine monomer, andamphoteric ion pair monomer. Nonionic monomer, anionic monomer, andcationic monomers are preferred. The representative nonionic monomersinclude vinyl amide, acryloylmorpholine, acrylate, maleic anhydride,N-vinylpyrrolidone, vinyl acetate, N-vinyl formamide and theirderivatives, such as hydroxyethyl (methyl)acrylate CH2=CR—COO—CH2CH2OH(I) and CH2=CR—CO—N(Z1)(Z2) (2) N-substituted (methyl)acrylamide (II).R═H or Me; Z1=5-15C alkyl; 1-3C alkyl substituted by 1-3 phenyl, phenylor 6-12C cycloalkyl (both optionally substituted) and Z2=H; or Z1 and Z2are each 3-10C alkyl; (II) is N-tert. hexyl, tert. octyl, methylundecyl,cyclohexyl, benzyl, diphenylmethyl or triphenyl acrylamide. The vinylamide is preferred nonionic monomer. Examples of vinyl amide includeacrylamide, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide.The representative anionic monomers include polymerizable organic acidsand their salts, and quaternary salts. The organic acids are preferredanionic monomer. Examples of organic acids include acrylic acid,methacrylic acid, maleic acid, itaconic acid, acrylamido methylpropanesulfonic acid, vinylphosphonic acid, styrene sulfonic acid. Therepresentative cationic monomers include quaternary ammonium or acidsalts of vinyl amide, vinyl carboxylic acid, methacrylate and theirderivatives. The quaternary ammonium salt derivatives from acrylamide oracrylic acid are preferred cationic monomer.

The term “Controlled monomer” refers to kinetically controllabledecomposition of monomers, wherein vinyl or allyl groups are bridged byone or more ethers, esters, azos, and amides, or other decomposablemoieties. Representative controlled monomers include [CR₁R₂═CR₃—CO-]nesters of di, tri, or tetra alcohols (I), [C R₁R₂═C R₃—O-]n esters ofdi, tri, or tetra functional acids (II), [C R₁R₂═CR₃—CR₄R₅—O]n esters ofdi, tri, or tetra functional acids (III), [CR₁R₂═CR₃—CO-]m amides (IV),[C R₁R₂═C R₃—]₂ of bisazo (V), [C R₁R₂═C R₃—CR₄R₅—]₂ of bisazo (VI), andthe derivatives of (I)-(VI). R₁═H or Me, R₂═H or Me, R₃═H or Me, R₄═R₅═Hor Me, n=2, 3, or 4, m=2, 3, or 4. Alcohols in (I) includeethyleneglycol, polyethyleneglycol, ethoxylated trimethylol, ethoxylatedpentaerythritol, and their derivatives. Typical controlled monomers inclass (IV) include N-tert. hexyl, tert. octyl, methylundecyl,cyclohexyl, benzyl, diphenylmethyl, triphenyl diacrylamides,diacrylamide, methacrylamide, piperazine diacrylamide, and theirderivatives. Preferred controlled monomers include water solublediacrylates and polyfunctional vinyl derivatives of a polyalcohol. Morepreferred controlled monomers include polyethylene glycol diacrylates.The monomers and controlled monomers may be polymerized and cross-linkedin a non-emulsion aqueous solution.

The term “Aqueous solution” refers to water, buffer solvent, or othernon-oil and non-surfactant solutions. The preferred solvent for aqueoussolutions is deionized water.

The term “Stable cross-linker” refers to aluminum salt, zirconium salt,chromium salt or organic cross-linker. The organic cross-linkers, suchas methylenebisacrylamide, hexamethylenetetramine, phenol aldehyde, arepreferred. The stable cross-linker is optional according to specificsubterranean conditions.

The initiators (e.g. ammonium persulfate, potassium persulfate, sodiumpersulfate, sodium bromate, sodium bisulfite, or mixture), optionallywith bases (e.g. sodium carbonate, sodium bicarbonate, sodiumhydroxide), reducing promoters (e.g. potassium metabisulfite, sodiumsulfite, thionyl chloride, thionyl bromide), regulators (e.g. alcohols),stabilizers (e.g. phenol, m-dihydroxybenzene, hydroquinone), chelatingagents (e.g. ethylene diamine tetra acetate), thermal agents (e.g.2-acrylamido-2-methyl propane sulfonic acid), chain-transfer agents(e.g. thiols, formic acid and alkali metal formates such as sodiumformate), oxygen scavengers (e.g. sodium sulfite, sodium bisulfite,sodium thiosulfate, sodium lignosulfate, ammonium bisulfite,hydroquinone, diethylhydroxyethanol, diethylhydroxylamine,methylethylketoxime, ascorbic acid, erythorbic acid, and sodiumerythorbate), pH adjusters (e.g. sodium or potassium hydroxide), and gelstrength modifiers (e.g. bentonite, lignocellulose, clay,montnorillonite, diatomite, kaolinoite, other fillers, or mixture), areemployed to initiate the polymerization reaction.

In preparing the starting reaction mixture, the compounds to bepolymerized are dissolved within an aqueous solution. The amount ofaqueous solution, such as deionized water, may vary, but typically from15 to 70% of the total weight of the initial reaction solution. Theamount of monomers may vary, but typically are from 5 to 60% of thetotal weight of start reacting solution. The amount of controlledmonomers may vary, but typically is from 0.01 to 30% of the total weightof the initial.reactinon solution. Depending upon the amount of totalmonomers, the stable cross-linker is typically from 0 to 5%, and the gelstrength modifier is typically from 0 to 60%. The caustic component isoptional to hydrolyze certain monomers, such as acrylamide, and itsamount of use may vary, but typically from 0 to 10%. The pH adjustersmay be necessary. The typical pH range of reacting solution is 6.5 to11. The reducing promoters, regulators, stabilizers, chelating agent,thermal agent, chain-transfer agent, oxygen scavenger are optionalaccording to the specific injection water and subterranean formation,and their amounts of use may vary. The order of addition for thereactants may vary; the typical order is the least polar compound firstto ensure it can be dissolved completely, then followed by more polarcompounds.

After the initial reaction mixture is agitated, at an ambienttemperature, typically from 15 to 30 degree C., the initiator orinitiators mixture is then slowly added into the dynamically mixed,sheared or oscillated reacting solution to achieve a homogenizedreacting condition. The amount of initiator may vary according to themonomers concentration, but typically from 0.01% to 0.2%. Because of theexothermic nature of the reaction initiated by the addition of theinitiators, evidence of the reaction is inferred by an increasedtemperature. Preferably the reaction is kept at the initial temperatureby means of having the reactor jacketed with a cooling fluid, or havingthe reactor surrounded by a vessel containing a circulating fluid. Agradual increase of the temperature of the reacting system is alsoacceptable. The result of the reaction process will result in a fine gelready for the post-treatment. The polymerizing and cross-linkingreaction are preferably carried out in oxygen free or in a reducedoxygen environment. However, short exposure to air is also acceptable.

The reaction can be performed in either a batch process or continuousprocess. Due to the fast polymerization reaction, typically severalminutes, the continuous process is preferred for medium to large scaleproduction. The deoxygenated monomers and supplemental materials arecontinuously pumped to a reaction vessel, and the reacted gel iscontinuously transferred away from the vessel. The gel is squeezedthrough small holes and cut to small particles or lumps for stepwisebaking, breaking, sieving post-treatments. The baking temperature mayvary according to the specific formulation, but the typical bakingtemperature is 15 to 20 degree C. lower than the decomposing temperatureof controlled monomers used in the formulation.

For small to medium scale production, the batch process is alsopreferred. The initial reacting solution, mixed monomers andsupplemental materials, is deoxygenated with inert gas, such asnitrogen, for about 30 to 50 minutes. Polymerization is initiated atroom temperature. The temperature typically rises to about 60 degree C.or higher by the heat released during polymerization. The polymerizedmixture is typically kept at that higher temperature, usually from 65 to80 degree C. to complete the reaction, resulting in production of softgel lumps. The gel lumps are dried on trays in an oven, and then areground to desirable sizes.

The size reduction of resulting polymeric gel particles can be achievedby mechanical methods (e.g. fluid energy or jet mills, stirred mediamills, ball mills, colloid mills, vibrating mills, rotor mills, cuttingmills, disc mills, jaw crushers, and mortar grinders), physical methods(e.g. spry drying) or chemical methods (e.g. polymerization insuspension). The mechanical grinding approaches by jet mill, ball milland colloid mill are preferred. The reported data indicates thatindustrial scale ball mill can grind hard, brittle materials under 1micron in size (e.g. Planetary ball mill by Retsch). The in-house testdescribed in an example in this application shows the dry gel particleafter being ground in a laboratory scale ball mill jar, can pass througha 400 mesh sieve, an opening of less than 37 micron diameter. Anindustrial scale colloid mill can grind colloid particles down to 1micron in diameter, and an in-house test shows the gel particlesuspension, after grinding in a laboratory colloid mill, can pass 200mesh sieve, less than 74 micron diameter, under 20 psi positivepressure.

Due to the characteristics of the size of initial particle, itshydrophilic nature, and that it contains controlled monomer that willdecompose to allow the particle to swell in a predictable manner, thecomposition of this invention can propagate far into the reservoir.

In a preferred aspect of this embodiment, this CPG composition is addedto injection water as part of a secondary water recovery process,tertiary carbon dioxide injection, chemical, or air injection forrecovery of hydrocarbon from subterranean sandstone or carbonateformation. This will provide controlling the near well-bore and in-depthformation conformance vertically and laterally by selectively blockingthe high water channels. The composition can be added in an amount fromabout 50 to 20,000 ppm, preferably from about 500 to 5000 ppm and morepreferably from about 1000 to 3000 ppm based on solid content, withproduced water, sea water, or fresh water.

The forgoing may be better understood by reference to the followingexamples, which are presented for purposes of illustration and are notintended to limit the scope of this invention.

EXAMPLES Example 1 Preparation of Sample 27

In the present example, a single aqueous phase was prepared by adding8.25 g acrylamide, 21.75 g sodium salt of 2-acrylamido-2-methylpropanesulfonic acid, 0.386 g polyethylene glycol 200 diacrylate, and 0.0004 gmethylene bisacrylamide to 30.6 g deionized water with then mixing. Atan ambient temperature of 15-30° C., an initiator mixture of 400 μl 5%sodium bromate and 400 μl 5% sodium bisulfite was added slowly to thesolution with strong mixing. Within about 5 minutes, the reaction ofpolymerization took place with heat released, resulting in a fine gel.

Example 2 Preparation of Sample 31

In this example, the procedure of example 1 was repeated except that6.10 g polyethylene glycol 200 diacrylate and no methylene bisacrylamidewere added to the formula. All other components and reaction conditionsremained the same.

Example 3

Comparison of swelling behavior of Sample 27 versus Sample 31demonstrates the controllability the swell time and extent with ourcomposition.

Sample 27 and Sample 31 suspensions were both prepared at aconcentration of 1 wt % in distilled water and had the pH adjusted to bebetween 8 to 9. A portion of each suspension was aged at 40 degree C.and at 60 degree C. for 2 days. The results are shown below:

Temperature (Centigrade) Sample 27 Sample 31 40 fluid fluid 60 stiff gelfluid

These results demonstrate that the composition of the Sample 27 issuitable for an application where the controlled monomer is designed todecompose within 2 days at 60 degree C. Furthermore, the fact that theSample 27 remains in a fluid state over the same aging time at 40 degreeC. indicate that for Sample 27 the mechanism for the loss ofeffectiveness of the controlled monomer, thereby causing particleexpansion and a gel to form is related to its exposure to a greaterextreme in temperature to 60 degree C. And Sample 31 is suitable when alonger time delay before significant particle expansion and gelation isdesirable.

Example 4

Grinding of Sample 27 can reduce size so that it may have a smalldiameter and thereby pass through smaller pore holes.

Sample 27 particles (described in Example 1 and Example 3) were added toa 0.3 wt % NaCl solution at a concentration of 1000 ppm. Thisparticulate suspension was added to a pressure vessel. A nitrogen gasline was connected to the top of the pressure vessel and the gaspressure was adjusted to 20 psi. A valve at the bottom of the vessel wasopened and the fluid exited and passed through a 200×200 mesh metalscreen mounted in a sealed holder. After injection of approximately 100ml of the particle suspension, the screen was inspected and found tohave a significant coating of the particle gel on the entire surface.

Next a portion of this same Sample 27 suspension initially made to aconcentration of 1000 ppm in a 0.3 wt % NaCl brine was added to alaboratory colloidal mill and exposed to 60 minutes of grinding time.This suspension of particles after grinding also were passed through aclean 200×200 mesh screen under 20 psi of driving gas pressure. In thiscase the screen has a much cleaner appearance with only slight evidenceof any solids accumulation in or on the metal screen.

This example illustrates it is possible to reduce the size of theseparticles significantly by grinding. Because the hole size in a 200×200mesh screen is about 75 microns in size, this demonstrates it ispossible to grind these particles to a size less than 75 microns. Basedon a rule of thumb that particles must have a diameter less thanone-third the hole size to pass thoroughly successfully, it is estimatedthat the 60 minutes of grinding reduced the average particle size toabout 25 microns in diameter. The ground particles maintain the samecomposition and have the same delayed swelling behavior as for theoriginal particles.

Example 5

The particles created are strongly hydrophilic and will remain primarilyin the water phase.

The Sample 27 particles described in Example 1 were added as a 0.5 wt %suspension into a distilled water solution of 80 milliliters volume.Next, this 80 milliliters of particle suspension fluid was poured into aglass separatory funnel, followed by 80 milliliters of n-decane. Thefunnel was shaken by hand vigorously for 5 minutes, and then leftstanding for overnight to allow separation of the aqueous andhydrocarbon phases. Next, the bottom aqueous layer was drained off fromthe separatory funnel into a wide dish. This pre-weighed dish was heateduntil all of the liquid has evaporated. After cooling, the dish wasre-weighed to determine the mass of solid particles remaining in theaqueous phase taken from the separatory funnel. By this method, over 95%of the initial mass of the particles from Sample 27 remained in theaqueous phase. This is an insignificant decrease, and is nearly the samemass of particles as the starting amount. These results confirm that thesuspended particles are hydrophilic in nature and have a much strongeraffinity for the aqueous phase than a hydrocarbon phase.

Cited Patents

-   CN Pat. No. 1,251,856A May 2000 Liu et al.-   CN Pat. No. 1,552,793A December 2004 Wu-   CN Pat. No. 1,796,484A July 2006 Li-   CN Pat. No. 1,439,692A September 2003 Li et al.-   U.S. Pat. No. 5,662,168 September 1997 Smith-   U.S. Pat. No. 5,465,792 November 1995 Dawson et al.-   U.S. Pat. No. 5,735,349 April 1998 Dawson et al.-   U.S. Pat. No. 6,454,003B1 September 2002 Chang et al.-   U.S. Pat. No. 6,729,402B2 May 2004 Chang et al.-   U.S. Pat. No. 6,984,705B2 January 2006 Chang et al.

Other Literature Cited

-   Liu, Y., et al,“Application and Development of Chemical-Based    Conformance Control Treatments in China Oilfields,” paper SPE 99641    presented at the 2006 SPE/DOE Symposium on Improved Oil Recovery    held in Tulsa, Oklahoma, U.S.A. Apr. 22-26, 2006.-   Bai, B., et al, “Preformed Particle Gel for Conformance Control:    Transport through Porous Media and IOR Mechanisms,” paper SPE 89468    presented at the 2004 SPE/DOE Fourteenth Symposium on Improved Oil    Recovery held in Tulsa, Oklahoma, U.S.A., Apr. 17-21, 2004.

1. A method of conformance control for oil and gas production by usinggel-forming materials comprising preformed particles, wherein theparticles have a controlled delay time before forming a gel andexpanding significantly.
 2. The method of claim 1, wherein the size ofthe preformed particles ranges from 10 microns to 5 millimeters indiameter.
 3. The method of claim 1 wherein the preparation of gelsfurther comprises forming cross-linked expandable polymeric particles.4. The method of claim 1, wherein said method further comprisespolymerizing one or more polymerizable monomers, in concentrations offrom about 5 to 60 % of reactants, under free radical initiator-formingconditions in the presence of about 0.01% to 30% of controlled monomersand 0 to about 5% of stable cross-linkers in aqueous solution.
 5. Themethod of claim 4, wherein said method further comprises agents selectedfrom the group consisting of: bases, reducing promoters, regulators,stabilizers, chelating agent, thermal agents, chain-transfer agents,oxygen scavengers, pH adjusters, and gel strength modifiers, in amountsof from 0 to about 60%.
 6. The method of claim 4 wherein the monomer isselected from the group consisting of: nonionic monomer, anionicmonomer, cationic monomer, zwitterionic monomer, betaine monomer, andamphoteric ion pair monomer.
 7. The method of claim 4 wherein thenonionic monomers are selected from the group consisting of: vinylamide, acryloylmorpholine, acrylate, maleic anhydride,N-vinylpyrrolidone, vinyl acetate, N-vinyl formamide and theirderivatives.
 8. The method of claim 4 wherein the nonionic monomers areselected from the group consisting of: hydroxyethyl (methyl) acrylateCH2=CR—COO—CH2CH2OH (I) and CH2=CR—CO—N(Z1)(Z2) (2) N-substituted(methyl)acrylamide (II), wherein R═H or Me; Z1=H or 5-15C alkyl; 1-3Calkyl substituted by 1-3 phenyl, phenyl or 6-12C cycloalkyl (bothoptionally substituted) and Z2=H; Z1 and Z2 are each 3-10C alkyl; (II)is N-tert. hexyl, tert. octyl, methylundecyl, cyclohexyl, benzyl,diphenylmethyl, triphenyl Acrylamide; and their derivatives.
 9. Themethod of claim 4 wherein the anionic monomers are salts of unsaturatedorganic acids, including acrylic acid, methacrylic acid, maleic acid,itaconic acid, acrylamido methylpropane sulfonic acid, vinylphosphonicacid, styrene sulfonic acid and their derivatives.
 10. The method ofclaim 4 wherein the cationic monomers include quaternary ammonium andacid salts of vinyl amide, vinyl carboxylic acid, methacrylate and theirderivatives.
 11. The method of claim 4 wherein the controlled monomersinclude: a. [CR₁R₂═CR₃—CO-]n esters of di, tri, tetra alcohols (I); b.[CR₁R₂═CR₃—O-]n esters of di, tri, tetra functional acids (II); c.[CR₁R₂═CR₃—CR₄R₅—O]n esters of di, tri, tetra functional acids (III); d.[CR₁R₂═CR₃—CO-]m amides (IV); e. [CR₁R₂═C R₃—]₂ of bisazo (V); f.[CR₁R₂═C R₃—CR₄R₅—]₂ of bisazo (VI); and, the derivatives of (I)-(VI),wherein R₁═H or Me, R₂═H or Me, R₃═H or Me, R₄═R₅═H or Me, n=2, 3, or 4,and m=2, 3, or
 4. 12. The method of claim 4 wherein the stablecross-linkers include aluminum salt, zirconium salt, chromium salt andorganic cross-linkers such as methylenebisacrylamide,hexamethylenetetramine, and phenol aldehyde.
 13. The method of claim 4wherein the aqueous solution includes water, buffer solvent, or othernon-oil and non-surfactant solutions and their derivatives.
 14. Themethod of claim 4 wherein the initiators are selected from the groupconsisting of: ammonium persulfate, potassium persulfate, sodiumpersulfate, sodium bromate, sodium bisulfite, and mixtures thereof. 15.The method of claim 5 wherein the bases are selected from the groupconsisting of: sodium carbonate, sodium bicarbonate, sodium hydroxideand their derivatives.
 16. The method of claim 5 wherein the reducingpromoters are selected from the group consisting of: potassiummetabisulfite, sodium sulfite, thionyl chloride, thionyl bromide andtheir derivatives.
 17. The method of claim 5, wherein said regulatorscomprise organic alcohols.
 18. The method of claim 5, wherein thestabilizers are selected from the group consisting of: phenol,m-dihydroxybenzene, and hydroquinone.
 19. The method of claim 5 whereinthe chelating agents are selected from the group consisting of: ethylenediamine tetra acetate (EDTA) and the like.
 20. The method of claim 5wherein the thermal agent comprises 2-acrylamido-2-methyl propanesulfonic acid and their derivatives.
 21. The method of claim 5, whereinthe chain-transfer agents are selected from the group consisting of:thiols, formic acid and alkali metal formates.
 22. The method of claim 5wherein the oxygen scavengers are selected from the group consisting of:sodium sulfite, sodium bisulfite, sodium thiosulfate, sodiumlignosulfate, ammonium bisulfite, hydroquinone, diethylhydroxyethanol,diethylhydroxylamine, methylethylketoxime, ascorbic acid, erythorbicacid, and sodium erythorbate.
 23. The method of claim 5 wherein the pHadjusters are selected from the group consisting of: sodium hydroxideand potassium hydroxide.
 24. The method of claim 5 where the gelstrength modifiers comprise clays, and more preferably comprise claysselected from the group consisting of: diatomite, bentonite,lignocellulose, bentonite, montmorillonite, kaolinoite, and mixturesthereof.
 25. A method of using mechanical or physical processes to grindcontrolled particle gel to sizes ranging from about 0.1 micron to 500micron in diameter for the purpose of conformance control in oil and gasproduction.
 26. The method of claim 25 wherein the mechanical processesare selected from: fluid energy or jet mills, stirred media mills, ballmills, colloid mills, vibrating mills, rotor mills, cutting mills, discmills, jaw crushers, and mortar grinders, to grind particle gels todesirable particle sizes.
 27. The method of claim 25 wherein processescan be performed under dry or wet conditions.
 28. The method of claim 25wherein said process can be repeated in multiple circulations, until thedesirable particle size is achieved.
 29. The method of claim 25 whereinthe physical processes further comprises spray drying.